給ListView設置emptyView
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使用ListView和GridView時，當列表為空時，默認是不顯示任何內容的，這樣對用戶非常不友好，這時我們就需要通過setEmptyView(View emptyView)來設置當列表為空時的提示。
emptyView簡單使用Demo
下面展示emptyView使用的簡單Demo。
activity_empty_list_view.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.littlejie.listview.EmptyListViewActivity">
<ListView
android:id="@+id/lv"
android:layout_width="match_parent"
android:layout_height="wrap_content"></ListView>
<!-- ListView的emptyView,默認不需設置其visiblity屬性設置為GONE -->
<!-- 當ListView為空時,emptyView會自動被設置為GONE -->
<!-- 當ListView不為空時,emptyView會自動被設置為VIBISIBLE -->
<LinearLayout
android:id="@android:id/empty"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:orientation="vertical">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="Empty" />
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="center"
android:gravity="center"
android:text="EmptyView可以是ViewGroup" />
</LinearLayout>
</LinearLayout>
EmptyListViewActivity.java:
public class EmptyListViewActivity extends Activity {
private ListView mLv;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_empty_list_view);
mLv = (ListView) findViewById(R.id.lv);
mLv.setAdapter(new ArrayAdapter<>(this,
android.R.layout.simple_list_item_1, generateString(0)));
mLv.setEmptyView(findViewById(android.R.id.empty));
}
private List<String> generateString(int num) {
List<String> list = new ArrayList<>();
for (int i = 0; i < num; i++) {
list.add("item " + i);
}
return list;
}
}
運行結果如下：

emptyView復雜使用Demo
前一個Demo講了emptyView的簡單使用方法，那如果我們要自定義emptyView或者emptyView的布局跟ListView不在同一個布局文件中呢？恩，你可能會說：直接調用setEmptyView(View emptyView)不行嘛，難道有啥不一樣？
看來，你還是too young too simple。直接調用的結果就是：emptyView根本就不會顯示！！！
新建一個ComplexEmptyListViewActivity.java:
public class ComplexEmptyListViewActivity extends Activity {
private ListView mLv;
private EmptyView mEmptyView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_complex_empty_list_view);
mLv = (ListView) findViewById(R.id.lv);
mLv.setAdapter(new ArrayAdapter<>(this,
android.R.layout.simple_list_item_1, Utils.generateString(0)));
mEmptyView = new EmptyView(this);
//此處是重點,如果不將mEmptyView添加進當前的ViewGroup,mEmptyView都不可見
//((ViewGroup) mLv.getParent()).addView(mEmptyView);
mLv.setEmptyView(mEmptyView);
}
}
布局文件activity_complex_empty_list_view.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
tools:context="com.littlejie.listview.EmptyListViewActivity">
<ListView
android:id="@+id/lv"
android:layout_width="match_parent"
android:layout_height="wrap_content"></ListView>
</LinearLayout>
EmptyView:
public class EmptyView extends LinearLayout {
public EmptyView(Context context) {
super(context);
init(context);
}
public EmptyView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
private void init(Context context) {
View view = LayoutInflater.from(context).inflate(R.layout.complex_empty_view, this);
}
}
complex_empty_view.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:text="假裝我是復雜的emptyView" />
</LinearLayout>
運行demo，你會發現ListView為空時，根本就沒顯示emptyView。這是為什么呢？因為emptyView根本就沒添加到當前Activity的布局中，所以即使設置了emptyView也不會顯示，解決方法就是把emptyView添加到當前Activity的布局中（ComplexEmptyListViewActivity注釋的內容）。
補充
細心的可能已經發現，在兩個demo中，我們都沒去設置emptyView的
visiblity屬性，這是為什么呢？其實看下源碼就知道了~當調用
setEmptyView(View emptyView)方法時，ListView會調用到updateEmptyStatus(boolean empty)，在這里系統會跟empty去判斷是否顯示emptyView。恩，就這么簡單~/** * Sets the view to show if the adapter is empty */ @android.view.RemotableViewMethod public void setEmptyView(View emptyView) { mEmptyView = emptyView; // If not explicitly specified this view is important for accessibility. if (emptyView != null && emptyView.getImportantForAccessibility() == IMPORTANT_FOR_ACCESSIBILITY_AUTO) { emptyView.setImportantForAccessibility(IMPORTANT_FOR_ACCESSIBILITY_YES); } final T adapter = getAdapter(); final boolean empty = ((adapter == null) || adapter.isEmpty()); updateEmptyStatus(empty); } /** * Update the status of the list based on the empty parameter. If empty is true and * we have an empty view, display it. In all the other cases, make sure that the listview * is VISIBLE and that the empty view is GONE (if it's not null). */ private void updateEmptyStatus(boolean empty) { if (isInFilterMode()) { empty = false; } if (empty) { if (mEmptyView != null) { mEmptyView.setVisibility(View.VISIBLE); setVisibility(View.GONE); } else { // If the caller just removed our empty view, make sure the list view is visible setVisibility(View.VISIBLE); } // We are now GONE, so pending layouts will not be dispatched. // Force one here to make sure that the state of the list matches // the state of the adapter. if (mDataChanged) { this.onLayout(false, mLeft, mTop, mRight, mBottom); } } else { if (mEmptyView != null) mEmptyView.setVisibility(View.GONE); setVisibility(View.VISIBLE); } }